Inspired by the cult novel from author Philip K Dick, 'The Man in the High Castle' has become Amazon's most-streamed original series to date since its launch in October.

Set in an alternate history where Germany won World War II and the United States remains under Nazi and Imperial Japanese rule, the series has attracted glowing reviews - and a fair bit of controversy.

With dark, brutal relish, actor Rufus Sewell plays Nazi officer and family man John Smith. In a candid new interview, he speaks to Digital Spy about the show's contentious subject matter, the "blandness" of network television - and why, for the first time ever, he's happy for a show of his to be renewed...

Congratulations on the success of The Man in the High Castle - it's now Amazon's most-watched original series.

That's very nice to hear. I was offered a part on Amazon Prime more than a year ago - and, at the time, it felt like being offered a part in something being done by WH Smith's! But everything changes so quickly - and now, of course, when you say you're doing something on Amazon Prime, people know it's a really cool thing.

I mean, the fact that Amazon had said yes to the idea of this series, when so many people had said no, showed that they had real balls. They were prepared to make an enormous statement and take a risk. I think that's something that we all felt while filming: that we were all very proud to be involved in something that - succeed or fail - was ambitious in that way.

The way Amazon Prime video works, the fate of a series is decided by viewer reaction to the pilot - how was that for you?

I mean, the idea that it's completely in the hands of the public... I don't think that's entirely true. That's one of the indicators - it's one of the things they take into account. But there's all sorts of other strange things they look at in determining their decision - though a large part of it is the audience reaction.

I do think that the audience reaction was so strong to 'The Man in the High Castle' pilot that even if Amazon Prime had not really liked it, there would've been a certain pressure for them to pick it up. Because otherwise it just makes a joke of the whole idea!

There's been a lot of talk about how 'traditional' television compares to streaming shows. Is there a marked difference for an actor?

Yes - very much so. I mean, I've only had one experience with doing a series on network television in America and that was quite a salutary lesson [he starred in 'Eleventh Hour' on CBS in 2008].

You think you've been offered a job by one group of people... and then you realise that they are really answering to another group - a much larger, more powerful group of faceless bureaucrats. I remember doing this American TV series and having people coming to visit me, asking me if I could smile more! Because they're trying to appeal to the widest possible base - including idiots!

Especially with the advent of cable, and now downloading and streaming, it's become more and more pronounced over the years: this difference between television made for people who've already subscribed... and television where they're selling the space between the advertising.

Networks feel a pressure to appeal to the widest common denominator at all times, so everything becomes so homogenised - the characters, the clothes, the music choices, the political choices espoused…

That's why everything has this same generic flavour. There is a financial reason for the blandness. But I think the reason that the popularity of these network shows is subsiding is because people can see the difference between relative artistic freedom, and that kind of constant compromise.

That doesn't mean that cable and streaming outlets don't have their market forces. Sometimes one can feel watching Starz or HBO that there is a certain 'tit per minute' quotient. Or a certain level of swearing that needs to be sustained in order to make people feel that they're getting their subscriptions' worth.

That can sometimes be a bit of a drag. But overall, in terms of quality, and in terms of the freedom that writers / directors / actors are afforded… it's so incredibly different from the way it is on network television in America.

Many actors say you have to like a character to play them. So how do you go about empathising with a character like John Smith?

This idea that you can't play a character without 'liking' them... I would describe that as 'from the tourist's brochure of acting'! But certainly you have to see it and feel it from your own perspective.

I was sent the first episode of 'The Man in the High Castle' and though I very much enjoyed reading it, I wasn't very attracted to the part. Because he seemed to be fulfilling a function - a function of the uber-villain, just absolute nothing but dark.

Then I discovered that John Smith wasn't in the book, so that compounded my suspicion that he'd been added. Because often when a character - a villain - is added, it's to perform a function: to weigh the thing down with a featureless representation of evil. So [the heroes] have something to work around. And I wasn't interested in that.

That's when Frank Spotnitz assured me that there was much more to this character. Especially as the season wore on, there were certain crises that would happen to him, that would really open up the character... and then it became interesting.

For me, what was interesting was that the original Nazis were totally uniformly degenerate - but as it swept up the country, it swept up a lot of people who, to all intents and purposes, had been good people up until then. They managed to tell themselves a story in which they were the good guys. And that was the majority of Germans. And the same thing I believe could happen - would happen - anywhere.

So in his own world, John Smith is an American hero and you can see evidence of that - he's genuinely a good father, he's a very loving man. But he also has a capacity to be unbelievably cruel and merciless and he thinks that's in the name of right.

Do you have to tread carefully though when you're making a series that deals in those themes?

Oh, absolutely. We were incredibly sensitive to it all the time. You don't do a show like this for four / five months without thinking about things like that all the time. It was the subject of pretty much all our conversations.

If there's anything it would be a benefit for us to learn, it's how it is possible for these things to happen. Not just in Germany in the 1930s, but anywhere in the world - and it can happen again if we don't look out.

In order to do justice to that subject, it might appear that we're condoning things, or normalising things. The idea of humanising someone like Smith might seem like an apology for Nazism, but in fact it's the opposite. In order to be responsible, we need to humanise.

'The Man in the High Castle' has been renewed for a second season - and you've said this was the first time you wanted a show you were in to be picked up. Why so?

There's only really been once that I was in that situation - doing this American TV series called 'Eleventh Hour'. And that was something I was in two minds about. Because I wanted my friends to continue to work and I didn't want to be broke. But at the same time, I did feel very trapped in something that I wasn't entirely comfortable in. And that's the only time.

I did a thing called 'Zen' [for the BBC], but that was never really 'season one' - the attraction of that job was it was only supposed to be three episodes. So that wasn't a matter of going in for something that was supposed to be multi-seasonal, and it being cancelled. That was just something where it was finite and it stayed finite.

But this time… television has changed so much. Now the great work, artistically speaking, is happening in cable and streaming. So if I can find myself playing a multi-faceted character, in something that will go multi-seasonal, at my age, then I feel very privileged.

'The Man in the High Castle' is now available exclusively on Amazon Prime Video.